Collaborative Research: Testing Mechanical Models of Himalayan Orogenesis in NW India

喜马拉雅山和西藏是陆-陆碰撞的典型范例，因此，印支造山带是碰撞造山作用的范例和构造模式的试验场。一个压倒一切的构造问题是什么控制着造山带的构造演化。经典的逆冲发展模型（临界锥度模型）不排除地壳的薄弱部分，但建议这些不一致的工作，以诱导流动;相反，最近的热-力学模型（通道流动模型）处理的中地壳和下地壳深刻薄弱，并与侵蚀主导变质和构造的发展。该项目由亚拉巴马大学和博伊西州立大学的研究人员与喜马拉雅地质学瓦迪亚研究所的科学家合作开展，旨在通过利用这些模型预测的完全不同的压力-温度-时间运动学历史来区分这两种对立的观点。具体而言，该小组将在印度西北部的喜马偕尔邦-北兰查尔邦进行综合的构造、岩石学、地层学和地质年代学调查，以解决有关喜马拉雅逆冲运动和构造演化的三个基本问题：（1）地层和构造包如何与尼泊尔的沿着走向相关？野外测绘和构造分析将允许从尼泊尔到印度的地层对比，并通过平衡横截面确定逆冲几何形状和缩短量。薄片、Nd同位素和碎屑锆石分析有助于确定主要的岩石构造单元，这对不同逆冲岩席的准确定位至关重要。(2)喜马拉雅主要逆冲断层的压力-温度-时间演化是怎样的？独居石颗粒通过电子和离子微探针的岩石学和年代学特性将涉及到每个岩石的温度-时间演化，产生的逆冲运动的时间和加热和冷却的速率。新的更准确和精确的微量元素温度计用于确定峰值压力-温度条件和分布及路径。(3)喜马偕尔邦-北兰查尔邦的运动学历史与尼泊尔相比如何？本研究的主要目的是解决现代构造学中一个基本而有争议的问题：地壳在造山过程中的整体行为是由临界锥模型还是最近的通道流模型更好地解释。临界锥度理论认为，楔形的变形岩石块在刚性的挡块前面发展，导致向前传播的逆冲断层。通道流动模型认为，集中在山脉前沿的侵蚀力变形的一个薄弱的通道中，在中地壳和部分熔融岩石隧道走向山脉前沿。该项目还支持研究生和本科生的研究教育，促进美国和印度机构之间的科学合作，并支持地球科学教授中代表性不足的群体。

The Himalaya and Tibet stand as the type example of a continent-continent collision, thus the Indo-Asian orogen serves as a paradigm for collisional orogenesis and a testing ground for tectonic models. One overriding tectonic issue is what controls the structural evolution of an orogen. Classic models of thrust development (the critical taper model) do not preclude weak portions of the crust but suggest that these do not work in concert to induce flow; in contrast recent thermal-mechanical models (channel flow models) treat the middle and lower crust as profoundly weak and in concert with erosion dominate metamorphic and structural development. This project, carried out by researchers from the University of Alabama and Boise State University in collaboration with scientists at the Wadia Institute of Himalayan Geology, aims to discriminate between these two opposing views by exploiting the radically different pressure-temperature-time kinematic histories predicted by these models. Specifically, the team will carry out integrated structural, petrologic, stratigraphic, and geochronologic investigations in the Himachal-Uttaranchal in northwestern India to address three basic questions regarding Himalayan thrust transport and tectonic evolution: (1) How do stratigraphic and structural packages correlate along strike from Nepal? Field mapping and structural analysis will permit stratigraphic correlations from Nepal to India and define thrust geometries and shortening amounts via balanced cross sections. Thin section, Nd isotope, and detrital zircon analysis will help define major lithotectonic units, which is critical to accurate placement of different thrust sheets. (2) What was the pressure-temperature-time evolution of the major Himalayan thrusts? Petrologic and chronologic characterization of monazite grains via electron and ion microprobes will be related to the temperature-time evolution of each rock, yielding timing of thrust movement and rates of heating and cooling. New more accurate and precise trace element thermometers are use to determine peak pressure-temperature conditions and distributions and paths. (3) How does the kinematic history in Himachal-Uttaranchal compare with Nepal?The main purpose of this research is to address a fundamental and controversial question in modern tectonics: Is the overall behavior of the crust during mountain building better explained by the critical taper model or the more recent channel flow model. The critical taper theory argues that a wedge-shaped mass of deformed rocks develops in front of a rigid backstop resulting in forward propagating thrust faults. The channel flow model argues that focused erosion at the mountain range front forces deformation in a weak channel in the mid- to lower crust and partially molten rocks tunnel toward the mountain front. This project also support the research education of graduate and undergraduate students, fosters improved scientific collaborations among institutions both within the United States and in India, and supports an underrepresented group among the geosciences professoriate.